The present invention relates to fan case liners for gas turbine engines and more Particularly to a fan case liner having an area structured to resist damage or denting caused by the impact of a foreign body, such as ice, birds or the like, which are hurled against the fan case liner by the rotating fan of the gas turbine engine.
Large turbo-fan gas turbine engines have a liner segment mounted within the fan case of the engine immediately aft of the fan. One function of the fan case liner is the suppression of engine noise. These liner segments are preferably constructed of lightweight materials which make them highly susceptible to foreign object damage when impacted by a high velocity object accelerated by the centrifugal force of the rotating fan.
Fan case liner damage or denting can be a particular Problem during aircraft operation in cold weather or in colder climates when weather conditions are favorable for the formation of ice. Ice can form and build-up on the spinner and fan blade roots when an aircraft is in a holding pattern and the fan is rotating at a relatively low speed. When the aircraft is given clearance to leave the holding pattern, the subsequent acceleration of the engine can cause the ice to shed from the spinner and root of the fan and to be hurled into the fan case liner causing damage or denting which can adversely affect the aerodynamic performance of the bypass duct of the turbo-fan engine.
A prior modification to a fan case liner to resist foreign body impact damage included providing a solid face sheet of fiberglass or metallic material backed by a honeycombed layer of aluminum or aluminum alloy having a higher density than the honeycombed layer in conventional fan case liners. This modification, however, resulted in an unacceptable weight increase.